RiPP Enzymes for Biosynthetically Derived Cyclic Peptide Libraries.

Peptide libraries, especially those featuring cyclic and other modified variants, are central in drug discovery and chemical biology. Traditional methods for their generation often rely on labor-intensive synthetic approaches with limited diversity or enzyme-mediated conversions, which are constrained by substrate specificity, scalability challenges, complex biosynthetic systems, and restricted functional group diversity. This mini-review highlights enzymes from ribosomally synthesized and posttranslationally modified peptide (RiPP) gene clusters, an expanding class of biocatalysts, as a alternative enzyme source. RiPP enzymes may address key limitations in modified peptide library production, particularly in cyclization. With regulatable allosteric activities and compatibility with short synthetic peptides under mild conditions, these enzymes could be seamlessly integrated into scalable, high-throughput workflows and in vitro systems. This mini-review provides a perspective on RiPP enzymes through the lens of synthetic peptide library users, exploring their potential for converting synthetic peptide libraries and outlining the key requirements for their broader application in generating chemically diverse, new-to-nature peptide scaffolds.